I happen to hugely enjoy the work of PG Wodehouse. Despite the usual comedic exaggerations of his descriptions of the early 20th century, he often reveals some interesting assumptions.
In a number of his books, the protagonist (through well meaning blackmail or some other benevolent trickery) demands that the antagonist cough up some cash (to enable a couple to get married or for some other happy scheme).
The antagonist protests that he doesn't have his cheque book with him viz,
"Five thousand!" cried Mr. Waring. "It's monstrous."
"It isn't," said Psmith. "It's more or less of a minimum. I have made inquiries. So out with the good old cheque-book, and let's all be jolly."
"I have no cheque-book with me."
"I have," said Psmith, producing one from a drawer. "Cross out the name of my bank, substitute yours, and fate cannot touch us." Mr. Waring hesitated for a moment, then capitulated. Psmith watched, as he wrote, with an indulgent and fatherly eye.
"Finished?" he said. "Comrade Maloney."
"Youse hollering fer me?" asked that youth, appearing at the door.
"Bet your life I am, Comrade Maloney. Have you ever seen an untamed mustang of the prairie?"
"Nope. But I've read about dem."
"Well, run like one down to Wall Street with this cheque, and pay it in to my account at the International Bank."
Could people really just manually amend someone else's cheque with the details of a totally different bank and account holder and expect the altered cheque to be honoured without question, or is this just exaggeration for comedic effect?
Not only that, but a check theoretically could be written on almost anything, certainly on any kind of paper. The concept of a "negotiable instrument" is that it's merely an instruction from an account holder to his agent (the bank) to take certain action (pay to the order of), and that instruction can then be traded among people as if it had intrinsic value. Even codified in the modern Uniform Commercial Code, the only legal requirements are the name of the payee, the dollar amount, the name of your bank, your signature, the date, and words of conveyance (like "pay to"). As a practical matter, in the modern world, you'll have trouble getting a merchant or lender to accept a check that won't move seamlessly through the banking/check clearing system. In addition, most banks now have provisions in their deposit contracts limiting the form of deposit slips and checks.
Well into the 1960s, it was common for grocery stores in small cities to have at the checkout books of "counter checks," blank checks having only the name of one of the local banks, and presumably by that time, the clearinghouse routing code for that bank (don't remember if magnetic ink was yet required). The customer filled in his name and account number by hand, and wrote the check for the amount of purchase.
I just finished a class on Payment Systems and perhaps I can shed some light on the topic. I would suggest for a text The History of the Law Merchant and Negotiability by P. Wilifred Thornely if you want further reading.
First, we need to discuss what a check is. A check is a negotiable instrument, specifically it is a draft drawn on a bank. A draft is order to pay someone something. A draft ordering a bank to pay someone is called a check. Checks grew out of the law merchant which was a universally recognized system by which commerce was conducted.
As mercantilism arose, there became a need for a method of exchange that did not require you to carry around large amounts of money. Checks filled this role. A merchant traveling from England to Paris didn't want to carry coin, so he would bring checks.
Let's say a Parisian goes up to an English merchant in Paris, we will call the merchant Danforth, and buys a bunch of pelts. The Parisian writes a check with negotiable language: Pay to the Order of Danforth. He signs the check. After a day's business, the Englishman needs to buy provisions for the crew of his ship, so he goes to a shop. He takes out the Parisian's check and writes on the back, Pay to the Order of The Storekeeper, and then signs Danforth under it. The Storekeeper will then use the check in the same way until someone decides to present the check at the Parisian's bank for payment. Every time the check is given to someone else, called a negotiation, and is made payable to the order of someone not the original payee, and signed by the previous party, called an endorsement, the person taking the check becomes a holder with all the rights of the person who negotiated the check to him. Checks were freely transferable and as good as cash.
Until electronic checking, this kind of check transfer was very common. Actually until 9/11, checks in the United States were physically transferred between banks, taking up to two weeks before they returned account holder's bank. After 9/11, it was realized that this was not a safe means of transporting checks, so now all transfers are digital. In 1916, it would be common for someone to present a check which had gone through multiple hands at a bank. A check may have passed through several hands before being paid.
Could a check be altered? Sure. Generally, per the Law Merchant, checks were only enforceable per their original terms. If such an issue were brought to a court, parol evidence, that is oral evidence, and documents could be brought in as evidence to prove the original terms of a check. In bringing such a claim, the bank would sue the last holder of a check who would sue the previous endorser in turn. In the case of a forgery, the party who forged the check would be nowhere to be found. Who bears the loss? Generally, courts would make the party who was in the best position to prevent further loss due to the forgery liable, usually the party who accepted the forged check. Why does this matter? Because checks were as good as cash and were freely transferred between people.
In your example, it appears that both parties would go to the bank together. I'm not certain of the rest of the context. A check though could be written on any piece of paper as long as the signature was on the bottom right and all the other information necessary to fulfill the obligation was on the check. A bank very well may accept the altered check if the check had all the proper endorsements, but if it aroused enough suspicion the bank would perhaps not honor it or simply require a blank check to be written.
Checks were much more highly regarded than today, and the law was someone more flexible. It is quite likely that the bank would simply present a blank check, have the payor fill in the information, endorse it, and complete the transaction that way.